Someone who does not have a sexual preference, or is in a relationship but does not have/enjoy sex. This mostly occurs with women, but the term "Unsexual" is usually only used when refering to males. Unsexuals can have relationships, but the relationships are usually pressuring because of sex. So the unsexual will either have sex to please the partner, or break up with the person. Almost all unsexuals end up alone, unless they find a partner that is also an unsexual.

Zelda: "So how long have you and Bill been dating?"
Mary: "6 months"
Zelda: "So how's the sex?"
Mary: "Umm... we don't have sex... Bill's an Unsexual"
Zelda: "Oh my, I'm so sorry"